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  • Other Sources  (2)
  • 2015-2019
  • 1990-1994  (2)
  • 1920-1924
  • 1993  (2)
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  • 2015-2019
  • 1990-1994  (2)
  • 1920-1924
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  • 1
    facet.materialart.
    Unknown
    Preliminary Ar-40/Ar-39 age spectrum and laser probe dating of the M1 core of the Manson Impact Structure, Iowa: A K-T boundary crater candidate (1993)
    In:  CASI
    Details
    Publication Date: 2019-08-14
    Description: Preliminary Ar-40/Ar-39 age spectrum and laser probe dating results from new drill core from the 35-km-diameter Manson Impact Structure (MIS), Iowa indicates a reasonable possibility that the MIS is a Cretaceous-Tertiary (K-T) boundary impact event. Several different types of samples from a melt-matrix breccia, a unit of apparent crater fill intersected by the M1 core, were analyzed. Ar-40/Ar-39 results from these samples indicate a maximum age for the MIS of about 65.4 plus or minus 0.4(2 sigma) Ma. Petrographic analyses of the samples indicate a high probability that all the dated samples from the melt-matrix breccia contain relict grains that were not entirely melted or degassed at the time of impact, suggesting that the actual age of the MIS could be somewhat younger than our preliminary results indicate. The results are consistent with a previously published age estimate of shocked microcline from the MIS central uplift of 65.7 plus or minus 1.0 Ma.
    Keywords: GEOPHYSICS
    Type: Lunar and Planetary Inst., Twenty-Fourth Lunar and Planetary Science Conference. Part 2: G-M; p 835-836
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
    facet.materialart.
    Unknown
    Lunar ferroan anorthosites - Mineralogy, compositional variations, and petrogenesis (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Results of a study of 16 samples from the anorthositic ferroan subgroup, or 'typical' ferroan anorthosites, are reported. The presence of heterogeneous, bimodal, and/or trimodal pyroxene compositions suggests that some of the anorthosites are polymict rocks; however, they are composed entirely of ferroan-anorthosite-suite lithologies. It is suggested that complex processes operated during the formation of the ferroan anorthosites. It is argued that original igneous compositional characteristics were altered during and/or after crystallization. Processes operative during anorthosite formation may have included some mixing of different melts, trapping of variable amounts of intercumulus liquid, postcrystallization redistribution of elements, or perturbations both during adcumulus growth and subsequent to crystallization by impact events.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 98; E5; p. 9089-9105.
    Format: text
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    NASA TECHNICAL REPORTS
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